The faunal (all fossil groups) species diversity curve for the Ordovician of Norway shows a strong and statistically significant cycle with a period of 12 to 14 million years. The cycle is supported by spectral analysis, autocorrelation and wavelet analysis. A spectral peak for a similar periodicity can also be seen in the diversity curve from Swedish collections, but is not statistically significant. The number of preserved species may be partly a reflection of differences in primary alpha diversity and differential preservation at different water depth. The causal mechanism for this periodicity is a matter of speculation, but may be sought in processes such as periodic tectonic or volcanic activity, or climate change by astronomical forcing.